Old movie costumes were often recycled by the studios. The B movies of the 40s were often made with costumes and sets left over from major productions. Sometimes they would actually tell B movie scriptwriters to come up with a story making use of costumes and sets left over from other films. I recall reading of an actor who complained of how badly the costumes for extras and bit players smelled because they weren’t laundered regularly.
The original “Star Trek” featured so many parallel Earth stories because it allowed the producers to cut costs by using sets and costumes already available at Universal studios.